Dummy dielectric fins for finfets with silicon and silicon germanium channels

ABSTRACT

A method for forming a semiconductor device includes forming first fins from a first semiconductor material and second fins from a second semiconductor material and encapsulating the first fins and the second fins with a protective dielectric. Semiconductor material between the first fins and the second fins is etched to form trenches. A dielectric fill is employed to fill up the trenches, between the first fins and between the second fins. The first semiconductor material below the first fins and the second semiconductor material below the second fins are oxidized with the first and second fins being protected by the protective dielectric. Fins in an intermediary region between the first fins and the second fins are oxidized to form dummy fins in the intermediary region to maintain a substantially same topology across the device.

BACKGROUND Technical Field

The present invention generally relates to semiconductor processing, andmore particularly to devices and methods for forming fin field effecttransistors (finFETs) with dummy dielectric fins to improve downstreamprocessing.

Description of the Related Art

Fin field effect transistors (finFETs) have satisfied the everdecreasing node size problem for semiconductor processing and havebecome a technology employed for 22 nm nodes and beyond. To furtherimprove finFET performance, particularly for mainstream bulk finFETs,two paths are being pursued. One path employs SiGe fins to boost p-typeFET (PFET) performance, and another path employs better isolation forjunction isolation. Two process issues include difficulty in cuttingdummy fins and fin induced topography, which causes patterningchallenges in downstream processing such as gate patterning.

SUMMARY

In accordance with an embodiment of the present principles, a method forforming a semiconductor device includes forming first fins from a firstsemiconductor material and second fins from a second semiconductormaterial and encapsulating the first fins and the second fins with aprotective dielectric. Semiconductor material between the first fins andthe second fins is etched to form trenches. A dielectric fill isemployed to fill up the trenches, between the first fins and between thesecond fins. The first semiconductor material below the first fins andthe second semiconductor material below the second fins are oxidizedwith the first and second fins being protected by the protectivedielectric. Fins in an intermediary region between the first fins andthe second fins are oxidized to form dummy fins in the intermediaryregion to maintain a substantially same topology across the device.

Another method for forming a semiconductor device includes etching aportion of a semiconductor substrate, the substrate including a firstsemiconductor material; growing a second semiconductor material in atrench formed by removing the portion; etching first fins in the firstsemiconductor material and second fins in the second semiconductormaterial in accordance with a dielectric mask; forming spacers onsidewalls of the dielectric mask and the first fins and the second finsto encapsulate the first fins and the second fins with a protectivedielectric; etching semiconductor material between the first fins andthe second fins to form trenches; filling the trenches, between thefirst fins and between the second fins with a dielectric fill; oxidizingthe first semiconductor material below the first fins and the secondsemiconductor material below the second fins such that the first andsecond fins are protected by the protective dielectric; and oxidizingfins in an intermediary region between the first fins and the secondfins to form dummy fins in the intermediary region to maintain asubstantially same topology across the device.

A semiconductor device includes first fins formed from a firstsemiconductor material in a first region and second fins formed from asecond semiconductor material in a second region. An intermediary regionis disposed between the first region and the second region. A pluralityof a dummy fins are disposed in the intermediary region and includedummy fins configured to maintain a fin topology across the intermediaryregion. A shallow trench isolation region is formed beneath the firstfins, the second fins and the dummy fins.

These and other features and advantages will become apparent from thefollowing detailed description of illustrative embodiments thereof,which is to be read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The disclosure will provide details in the following description ofpreferred embodiments with reference to the following figures wherein:

FIG. 1 is a cross-sectional view showing a substrate and a paddielectric layer thereon in accordance with an embodiment of the presentprinciples;

FIG. 2 is a cross-sectional view showing a device of FIG. 1 having aregion removed by etching in accordance with an embodiment of thepresent principles;

FIG. 3 is a cross-sectional view showing the device of FIG. 2 having theregion filled with an epitaxially grown material in accordance with anembodiment of the present principles;

FIG. 4 is a cross-sectional view showing the device of FIG. 3 havingfins etched from different materials in accordance with an embodiment ofthe present principles;

FIG. 5 is a cross-sectional view showing the device of FIG. 4 havingfins encapsulated by spacers and a cap dielectric in accordance with anembodiment of the present principles;

FIG. 6 is a cross-sectional view showing the device of FIG. 5 having theencapsulated fins employed as an etch mask to extend trenches into thesubstrate and epitaxially grown material in accordance with anembodiment of the present principles;

FIG. 7 is a cross-sectional view showing the device of FIG. 6 having adielectric fill formed in the trenches and in between the encapsulatedfins in accordance with an embodiment of the present principles;

FIG. 8 is a cross-sectional view showing the device of FIG. 7 showingoxidation of the substrate and epitaxially grown material beneath theencapsulated fins in accordance with an embodiment of the presentprinciples;

FIG. 9 is a cross-sectional view showing the device of FIG. 8 havingtrenches etched into an oxide layer beneath the encapsulated fins toform a shallow trench isolation region in accordance with an embodimentof the present principles;

FIG. 10 is a cross-sectional view showing the device of FIG. 9 havingfins masked to form an intermediary region and to remove encapsulatingmaterials from the fins in the intermediary region in accordance with anembodiment of the present principles;

FIG. 11 is a cross-sectional view showing the device of FIG. 10 havingdummy fins oxidized in the intermediary region in accordance with anembodiment of the present principles;

FIG. 12 is a cross-sectional view showing the device of FIG. 11 havingmasks and encapsulating material removed for the fins in accordance withan embodiment of the present principles;

FIG. 13 is a cross-sectional view showing the device of FIG. 12 having aconnected gate structure formed over the fins and dummy fins inaccordance with an embodiment of the present principles;

FIG. 14 is a cross-sectional view showing the device of FIG. 12 havingseparated gate structures formed over the fins and a dielectric cutregion formed over the dummy fins in accordance with an embodiment ofthe present principles; and

FIG. 15 is a block diagram showing methods for forming semiconductordevices in accordance with embodiments of the present principles.

DETAILED DESCRIPTION

In accordance with the present principles, methods and structures areprovided for forming dielectric-isolated Si and SiGe fins on a same chipand concurrently forming dummy dielectric fins to improve the topographyfor downstream processing. In one embodiment, the dummy dielectric finsare formed by a two-step oxidation process and remain in a finalstructure. Dummy oxide fins are formed from semiconductor fins and anoxide isolation is formed beneath the fins. The dummy oxide fins and theoxide isolation are formed concurrently during processing. The dummyoxide fins form a region that separates n-type devices from p-typedevices in a complementary metal oxide semiconductor (CMOS) device. Inaddition, the dummy oxide fins alleviate topography issues between Siand SiGe fins and facilitate downstream processing such as gatepatterning, planarization (chemical mechanical polishing (CMP)), etc.For example, CMP processing can be avoided as well as other processessince the dummy oxide structures alleviate topography issues.

It is to be understood that the present invention will be described interms of a given illustrative architecture; however, otherarchitectures, structures, substrate materials and process features andsteps may be varied within the scope of the present invention.

It will also be understood that when an element such as a layer, regionor substrate is referred to as being “on” or “over” another element, itcan be directly on the other element or intervening elements may also bepresent. In contrast, when an element is referred to as being “directlyon” or “directly over” another element, there are no interveningelements present. It will also be understood that when an element isreferred to as being “connected” or “coupled” to another element, it canbe directly connected or coupled to the other element or interveningelements may be present. In contrast, when an element is referred to asbeing “directly connected” or “directly coupled” to another element,there are no intervening elements present.

The present embodiments may include a design for an integrated circuitchip, which may be created in a graphical computer programming language,and stored in a computer storage medium (such as a disk, tape, physicalhard drive, or virtual hard drive such as in a storage access network).If the designer does not fabricate chips or the photolithographic masksused to fabricate chips, the designer may transmit the resulting designby physical means (e.g., by providing a copy of the storage mediumstoring the design) or electronically (e.g., through the Internet) tosuch entities, directly or indirectly. The stored design is thenconverted into the appropriate format (e.g., GDSII) for the fabricationof photolithographic masks, which typically include multiple copies ofthe chip design in question that are to be formed on a wafer. Thephotolithographic masks are utilized to define areas of the wafer(and/or the layers thereon) to be etched or otherwise processed.

Methods as described herein may be used in the fabrication of integratedcircuit chips. The resulting integrated circuit chips can be distributedby the fabricator in raw wafer form (that is, as a single wafer that hasmultiple unpackaged chips), as a bare die, or in a packaged form. In thelatter case, the chip is mounted in a single chip package (such as aplastic carrier, with leads that are affixed to a motherboard or otherhigher level carrier) or in a multichip package (such as a ceramiccarrier that has either or both surface interconnections or buriedinterconnections). In any case, the chip is then integrated with otherchips, discrete circuit elements, and/or other signal processing devicesas part of either (a) an intermediate product, such as a motherboard, or(b) an end product. The end product can be any product that includesintegrated circuit chips, ranging from toys and other low-endapplications to advanced computer products having a display, a keyboardor other input device, and a central processor.

It should also be understood that material compounds will be describedin terms of listed elements, e.g., SiGe. These compounds includedifferent proportions of the elements within the compound, e.g., SiGeincludes Si_(x)Ge_(1-x) where x is less than or equal to 1, etc. Inaddition, other elements may be included in the compound and stillfunction in accordance with the present principles. The compounds withadditional elements will be referred to herein as alloys.

Reference in the specification to “one embodiment” or “an embodiment” ofthe present principles, as well as other variations thereof, means thata particular feature, structure, characteristic, and so forth describedin connection with the embodiment is included in at least one embodimentof the present principles. Thus, the appearances of the phrase “in oneembodiment” or “in an embodiment”, as well any other variations,appearing in various places throughout the specification are notnecessarily all referring to the same embodiment.

It is to be appreciated that the use of any of the following “/”,“and/or”, and “at least one of”, for example, in the cases of “A/B”, “Aand/or B” and “at least one of A and B”, is intended to encompass theselection of the first listed option (A) only, or the selection of thesecond listed option (B) only, or the selection of both options (A andB). As a further example, in the cases of “A, B, and/or C” and “at leastone of A, B, and C”, such phrasing is intended to encompass theselection of the first listed option (A) only, or the selection of thesecond listed option (B) only, or the selection of the third listedoption (C) only, or the selection of the first and the second listedoptions (A and B) only, or the selection of the first and third listedoptions (A and C) only, or the selection of the second and third listedoptions (B and C) only, or the selection of all three options (A and Band C). This may be extended, as readily apparent by one of ordinaryskill in this and related arts, for as many items listed.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of exampleembodiments. As used herein, the singular forms “a,” “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises,” “comprising,” “includes” and/or “including,” when usedherein, specify the presence of stated features, integers, steps,operations, elements and/or components, but do not preclude the presenceor addition of one or more other features, integers, steps, operations,elements, components and/or groups thereof.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper,” and the like, may be used herein for ease of description todescribe one element's or feature's relationship to another element(s)or feature(s) as illustrated in the FIGS. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the FIGS. For example, if the device in theFIGS. is turned over, elements described as “below” or “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, the term “below” can encompass both an orientation ofabove and below. The device may be otherwise oriented (rotated 90degrees or at other orientations), and the spatially relativedescriptors used herein may be interpreted accordingly. In addition, itwill also be understood that when a layer is referred to as being“between” two layers, it can be the only layer between the two layers,or one or more intervening layers may also be present.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, these elements should notbe limited by these terms. These terms are only used to distinguish oneelement from another element. Thus, a first element discussed belowcould be termed a second element without departing from the scope of thepresent concept.

Referring now to the drawings in which like numerals represent the sameor similar elements and initially to FIG. 1, a device 10 is fabricatedin accordance with the present principles. Device 10 includes asubstrate 12. The substrate 12 in the embodiment shown and describedincludes a bulk substrate although other substrate structures may beemployed, e.g., a semiconductor on insulator (SOI) substrate. Thesubstrate 12 includes a semiconductor material and preferably includesSi or strained Si, although other materials e.g., SiC, SiGe, SiGeC, Sialloys, Ge, Ge alloys, etc. or any combination thereof, may be employed.

A pad dielectric layer 14 may be formed on the substrate 12. The paddielectric layer 14 may be grown or formed by implanting a high-energydopant into the bulk semiconductor substrate 12 and then annealing thestructure to form pad dielectric layer 14. In another embodiment, thepad dielectric layer 14 may be deposited. The pad dielectric layer 14may include a nitride, an oxynitride, a different dielectric material ora combination of one or more of these or other materials.

Referring to FIG. 2, the substrate 12 is masked and etched to form arecessed region 16. The recessed region 16 covers an area where adifferent substrate material will be deposited or grown. For example,region 15 includes a first material to be employed for a first type ofdevice and region 17 will include a second material to be used for asecond type of device. In one embodiment, the first material in region15 includes Si, and the second material to be formed in region 17 willinclude SiGe. Si can be employed for NFET devices while SiGe can beemployed for PFET devices.

Referring to FIG. 3, a material 18 is grown in recessed region 16. Inthe embodiment described, the material 18 includes SiGe, which isepitaxially grown. Epitaxy can be done by ultrahigh vacuum chemicalvapor deposition (UHVCVD), rapid thermal chemical vapor deposition(RTCVD), metalorganic chemical vapor deposition (MOCVD), low-pressurechemical vapor deposition (LPCVD), limited reaction processing CVD(LRPCVD), molecular beam epitaxy (MBE). Epitaxial materials may be grownfrom gaseous or liquid precursors. Epitaxial materials may be grownusing vapor-phase epitaxy (VPE), molecular-beam epitaxy (MBE),liquid-phase epitaxy (LPE), or other suitable process. The SiGe may havegermanium content in the range of 5% to 80%, or preferably between 20%and 60%.

The terms “epitaxial growth and/or deposition” and “epitaxially formedand/or grown,” mean the growth of a semiconductor material (crystallinematerial) on a deposition surface of another semiconductor material(crystalline material), in which the semiconductor material being grown(crystalline over layer) has substantially the same crystallinecharacteristics as the semiconductor material of the deposition surface(seed material). In an epitaxial deposition process, the chemicalreactants provided by the source gases are controlled, and the systemparameters are set so that the depositing atoms arrive at the depositionsurface of the semiconductor substrate with sufficient energy to moveabout on the surface such that the depositing atoms orient themselves tothe crystal arrangement of the atoms of the deposition surface.Therefore, an epitaxially grown semiconductor material has substantiallythe same crystalline characteristics as the deposition surface on whichthe epitaxially grown material is formed. For example, an epitaxiallygrown semiconductor material deposited on a {100} orientated crystallinesurface will take on a {100} orientation. In some embodiments, epitaxialgrowth and/or deposition processes are selective to forming onsemiconductor surface, and generally do not deposit material on exposedsurfaces, such as silicon dioxide or silicon nitride surfaces.

Referring to FIG. 4, a pad dielectric 14 is formed over thesemiconductor material 18. In one embodiment, the original paddielectric 14 is stripped, and a new pad dielectric 14 is formed overthe entire semiconductor surface. In another embodiment, the originalpad dielectric 14 is kept, and the new pad dielectric is formed over thesemiconductor 18. The pad dielectric 14 and the underlyingsemiconductors are patterned (e.g., using a sidewall imaging transfer(SIT) process) and etched (e.g., by a reactive ion etch (RIE) process)to form fins 20 and 22 in respective regions 15 and 17. The fins 20 and22 may be formed from the substrate 12 and material 18 in the respectiveregions 15 and 17.

Referring to FIG. 5, a spacer layer is conformally deposited over thedevice 10 followed by a RIE to remove the spacer layer from horizontalsurfaces and form spacers 24. The spacers 24 may include a same materialas the pad dielectric 14. Alternatively, the spacers 24 may include amaterial different from the pad dielectric 14. In one embodiment, thespacers 24 include a nitride, oxynitride or other suitable dielectricmaterial or combinations thereof. The spacers 24 cover sidewalls of thefins 20, 22.

Referring to FIG. 6, the RIE is continued to form trenches 26 betweenfins 20, 22. This is achieved by etching to remove substrate 12 materialbetween fins 20, and material 18 and substrate 12 between fins 22.

Referring to FIG. 7, a dielectric fill 28 is deposited over the device10 to fill in spaces between fins 20, 22. The dielectric fill 28 mayinclude an oxide material, such as silicon dioxide, although othermaterials may be employed. The dielectric fill 28 is planarized on thetop surface of the device 10 stopping on the pad dielectric 14.

Referring to FIG. 8, an oxidation process is performed by exposing thedevice 10 to an oxide environment at elevated temperatures. In oneembodiment, the oxidation includes exposure of the device to anoxidation environment containing oxygen or water vapor, at temperaturesof between about 600 degrees C. to about 1200 degrees C. for a fewseconds to a few hours. Oxidation species, such as, e.g., water steam,diffuse through the dielectric fill 28 and oxidize areas of thesubstrate 12 and material 18 not protected by pad dielectric 14 andspacers 24. After the oxidation process, the newly formed oxide, due tooxidation, in conjunction of the dielectric fill 28 form a dielectriclayer 30 below the fins 20, 22 across the device 10. The dielectriclayer 30 will be employed for shallow trench isolation (STI).

Referring to FIG. 9, a RIE is performed to form trenches 32 between fins20, 22. This is achieved by etching to remove dielectric fill 28 betweenfins 20, 22 and continue the etch into the dielectric layer 30. Thisforms an STI region 38 to isolate the fins 20, 22 from each other andfrom the substrate 12. The RIE forms pedestals 33 on which the fins 20,22 are supported.

Referring to FIG. 10, a fin cut mask 36 is applied to device 10 to coveractive fins 20, 22 and expose fins 40, 42 in a region 34 between regions44 and 46. The mask 36 is patterned using lithography to open up themask 36 in region 34 to expose fins 40 and 42. The mask 36 may include aresist material, a dielectric material or any other suitable maskmaterials. Region 44 includes fins 20, and region 46 includes fins 22.The region 34 provides a spacing between regions 44 and 46. Fins 40 and42 will be converted to dummy fins. The spacers 24 and pad dielectric 14are removed from the fins 40, 42 by a selective etch process inaccordance with the mask 36.

Referring to FIG. 11, the mask 36 is removed. The fins 40 and 42 areexposed to an oxidation process to oxidize the exposed fins 40, 42 toconvert the fins 40, 42 to oxide fins 48 and 50 (dummy fins). In oneembodiment, the oxide fin 48 includes an oxidized Si fin 48 and providesa silicon oxide dummy fin, and the oxide fin 50 includes an oxidizedSiGe fin and provides a silicon oxide dummy fin containing germanium.

Referring to FIG. 12, an etch process is performed to selectively removethe pad dielectric 14 and spacers 24 from the remaining fins 20, 22. Thedevice 10 includes fins 20, 22 and dummy fins 48, 50 across the device10. Since the fins 20, 22, 48, 50 are uniformly disposed across thedevice 10, no topography issues will arise in subsequent processing.Therefore, all topography related issues such as planarization (e.g.,CMP) dishing, etch loading effects, etc. are avoided.

Referring to FIG. 13, finFET fabrication continues with the formation ofa gate structure 56. The gate structure 56 includes a gate dielectric 52and a gate conductor 54. In preparation for the formation of the gatedielectric 52, a gate dielectric preclean process may be employed whichreduces (thins) the dummy oxide fins 48, 50. Oxide fins 48, 50 and fins20, 22 have the gate dielectric 52 conformally formed over the fins 20,22, 48 and 50. The gate dielectric 52 may include an oxide, a nitride, ahigh dielectric constant (high-K) material or combinations of these orother materials.

The gate conductor 54 includes conductive materials, such as, e.g.,polycrystalline or amorphous silicon, germanium, silicon germanium, ametal (e.g., tungsten, titanium, tantalum, ruthenium, zirconium, cobalt,copper, aluminum, lead, platinum, tin, silver, gold), a conductingmetallic compound material (e.g., tantalum nitride, titanium nitride,tungsten silicide, tungsten nitride, ruthenium oxide, cobalt silicide,nickel silicide), carbon nanotube, conductive carbon, graphene, or anysuitable combination of these materials. The conductive material mayfurther comprise dopants that are incorporated during or afterdeposition.

In the embodiment shown, the gate structure 56 is formed over the fins20 and 22 in different areas of the device 10. For example, fins 20 mayinclude Si for NFETs while the fins 22 include SiGe for PFETs. The NFETsand PFETs have a same gate structure (gates for NFETs and PFETs areconnected) formed over both device types.

Referring to FIG. 14, finFET fabrication continues with the formation ofgate structures 58 and 60. The gate structures 58, 60 include the gatedielectric 52 and the gate conductor 54. In preparation for theformation of the gate dielectric 52, a gate dielectric preclean processmay be employed which reduces (thins) the dummy oxide fins 48, 50. Oxidefins 48, 50 and fins 20, 22 have the gate dielectric 52 conformallyformed over the fins 20, 22, 48 and 50. The gate dielectric 52 mayinclude an oxide, a nitride, a high dielectric constant (high-K)material or combinations of these or other materials.

The gate conductor 54 may be deposited and patterned over each devicearea (e.g., over fins 20 for NFETs and over fins 22 for PFETs). Then, adielectric material 62 may be deposited and planarized. The dielectricmaterial 62 may include e.g., an oxide. Alternately, the dielectricmaterial 62 may be deposited and patterned followed the gate conductor54, which can be deposited and planarized. Alternatively, two separatedummy gates may be formed over fins 20 and 22. The dummy fins 20, 22 arecovered by dielectric material 62. The dummy gates are then removed andreplaced with high-k gate dielectric and gate conductor. In such a case,high-k gate dielectric does not present on dummy fins 48, 50. The dummyfins 48, 50 may be covered by dielectric 62 with an optional dielectricliner (e.g., gate dielectric or silicon nitride) between dummy fins anddielectric 62. The gate conductors 54 may include the same material ordifferent materials for each region (NFET region and PFET region). Theconductor 54 may include, e.g., polycrystalline or amorphous silicon,germanium, silicon germanium, a metal (e.g., tungsten, titanium,tantalum, ruthenium, zirconium, cobalt, copper, aluminum, lead,platinum, tin, silver, gold), a conducting metallic compound material(e.g., tantalum nitride, titanium nitride, tungsten silicide, tungstennitride, ruthenium oxide, cobalt silicide, nickel silicide), carbonnanotube, conductive carbon, graphene, or any suitable combination ofthese materials. The conductive material may further comprise dopantsthat are incorporated during or after deposition.

In accordance with the present principles, the dummy oxide fins 48, 50and oxide isolation layer 30 under the fins may be formed concurrently.In one embodiment, the dummy oxide fins 48, 50 may be formed whileoxidizing the layer 30 (in a single step). Dummy oxide fins 48 alleviatetopography changes between fins 20, 22 in different regions. By creatinga more uniform topology across the device, downstream processing issimplified by eliminating divots or other non-uniformities. In addition,gate patterning, planarization steps and other process steps can beeliminated.

Referring to FIG. 15, methods for forming semiconductor devices areillustratively shown. In some alternative implementations, the functionsnoted in the blocks may occur out of the order noted in the figures. Forexample, two blocks shown in succession may, in fact, be executedsubstantially concurrently, or the blocks may sometimes be executed inthe reverse order, depending upon the functionality involved. It willalso be noted that each block of the block diagrams and/or flowchartillustration, and combinations of blocks in the block diagrams and/orflowchart illustration, can be implemented by special purposehardware-based systems that perform the specified functions or acts orcarry out combinations of special purpose hardware and computerinstructions.

In block 102, first fins are formed from a first semiconductor material,and second fins are formed from a second semiconductor material. Thismay include etching a region of a substrate formed from the firstmaterial, and growing the second material in the region. Other methodsmay also be employed. In block 104, the first fins and the second finsare encapsulated with a protective dielectric. This may include a caplayer and spacers.

In block 106, semiconductor material is etched between the first finsand the second fins to form trenches. The fins encapsulated with theprotective dielectric can be employed as an etch mask. A pad dielectriccap on top and spacers may be employed for encapsulating the first finsand the second fins with the protective dielectric. The spacers can beformed on the pad dielectric cap and on sidewalls of the first fins andthe second fins.

In block 108, the trenches, spaces between the first fins and spacesbetween the second fins are filled with a dielectric fill. Thedielectric fill may be planarized. In block 110, the first semiconductormaterial below the first fins and the second semiconductor materialbelow the second fins are oxidized by exposing the device to an oxygenenvironment under elevated temperatures. The first and second fins areprotected by the protective dielectric during the oxidation. Thesubstrate and (epitaxially grown material in the substrate are convertedto dielectric material and form a dielectric layer beneath the fins.This dielectric layer isolates the fins from the substrate (e.g.,similar to a buried dielectric in a semiconductor-on-insulatorsubstrate).

In block 112, before oxidizing fins in the intermediary region, removingthe dielectric fill and over-etch to form shallow trench isolation (STI)regions below the first fins and the second fins. This forms pedestalson which the fins are supported. In block 114, fins in an intermediaryregion between the first fins and the second fins are exposed andoxidized to form dummy fins in the intermediary region to maintain asubstantially same topology across the device. In one embodiment, thefins in the intermediary region may be exposed and oxidized along withthe formation of the dielectric layer beneath the fins.

In block 116, the protective dielectric is removed from the first finsand the second fins. In block 118, a gate structure may be formed overthe first fins and the second fins. In block 120, the gate structure mayinclude a first gate structure over the first fins and a second gatestructure over the second fins. In block 122, the gate structure may beformed over the first fins and the second fins to connect the first finsand the second fins. In block 124, processing continues with theformation of interlevel dielectric layers, contacts, metallizations,etc.

Having described preferred embodiments for dummy dielectric fins forfinFETS with Si and SiGe channels (which are intended to be illustrativeand not limiting), it is noted that modifications and variations can bemade by persons skilled in the art in light of the above teachings. Itis therefore to be understood that changes may be made in the particularembodiments disclosed which are within the scope of the invention asoutlined by the appended claims. Having thus described aspects of theinvention, with the details and particularity required by the patentlaws, what is claimed and desired protected by Letters Patent is setforth in the appended claims.

1. A method for forming a semiconductor device, comprising: forming first fins from a first semiconductor material and second fins from a second semiconductor material, wherein the first semiconductor material is different from the second semiconductor material; encapsulating the first fins and the second fins with a protective dielectric; etching semiconductor material between the first fins and the second fins to form trenches; filling the trenches between the first fins and between the second fins with a dielectric fill; oxidizing the first semiconductor material below the first fins and the second semiconductor material below the second fins while the first and second fins are protected by the protective dielectric; and oxidizing fins in an intermediary region between the first fins and the second fins thus forming consecutive dummy fins in the intermediary region to create a uniform topology of fins with same heights across the device.
 2. The method as recited in claim 1, wherein forming the first fins from the first semiconductor material and the second fins from the second semiconductor material includes: etching a region of a substrate formed from the first material; and growing the second material in the region.
 3. The method as recited in claim 1, wherein the first fins and the second fins include a pad dielectric cap on top and wherein encapsulating the first fins and the second fins with the protective dielectric further includes: forming spacers on the pad dielectric cap and on sidewalls of the first fins and the second fins.
 4. The method as recited in claim 1, further comprising removing the protective dielectric from the first fins and the second fins.
 5. The method as recited in claim 4, further comprising forming a gate structure over the first tins and the second fins.
 6. The method as recited in claim 5, wherein the gate structure includes a first gate structure over the first fins and a second gate structure over the second fins.
 7. The method as recited in claim 5, wherein the gate structure is formed over the first fins and the second fins thus connecting the first fins and the second fins.
 8. The method as recited in claim 1, further comprising, before oxidizing fins in the intermediary region, removing the dielectric fill and etching thus forming shallow trench isolation regions below the first fins and the second fins.
 9. A method for forming a semiconductor device, comprising: etching a portion of a semiconductor substrate, the substrate including a first semiconductor material, wherein the first semiconductor material is different from the second semiconductor material; growing a second semiconductor material in a trench formed by removing the portion; etching first fins in the first semiconductor material and second fins in the second semiconductor material in accordance with a dielectric mask; forming spacers on sidewalls of the dielectric mask and the first fins and the second fins thus encapsulating the first fins and the second fins with a protective dielectric; etching semiconductor material between the first fins and the second fins thus forming trenches; filling the trenches, between s and between the second fins with a dielectric fill; oxidizing the first semiconductor material below the first fins and the second semiconductor material below the second fins while the first and second fins are protected by the protective dielectric; and oxidizing fins in an intermediary region between the first fins and the second fins thus forming consecutive dummy fins in the intermediary region to create a uniform topology of fins with same heights across the device.
 10. The method as recited in claim 9, further comprising removing the protective dielectric from the first fins and the second fins.
 11. The method as recited in claim 10, further comprising forming a gate structure over the first fins and the second fins.
 12. The method as recited in claim 11, wherein the gate structure includes a first gate structure over the first fins and a second gate structure over the second fins.
 13. The method as recited in claim 11, wherein the gate structure is formed over the first fins and the second fins thus connecting the first fins and the second fins.
 14. The method as recited in claim 9, further comprising, before oxidizing fins in the intermediary region, removing the dielectric fill and etching thus forming shallow trench isolation regions below the first fins and the second fins. 15-20. (canceled) 